The synthesis of methylpolydisilylazane is known in the art. See Gaul U.S. Pat. No. 4,340,619. Methylpolydisilylazane finds utility in the production of silicon nitride and silicon carbide containing ceramic fibers and the like. Methylpolydisilylazane is typically prepared by the reaction of a mixture of methylchlorodisilanes and hexamethyldisilazane to form trimethylchlorosilane and a partially trichloromethylsilylamino-endblocked methylpolydisilazane which contains unreacted chloride. The unreacted chloride content ranges from 3 to 6 weight percent. That chloride content is in the form of about 90 weight percent silicon-bonded chloride and about 10 weight percent ammonium chloride as determined by infrared spectrophotometry.
The residual chloride content is a major factor in decreasing the suitability of the methylpolydisilylazane polymer for use in the production of high strength ceramic fibers. Silicon-bonded chloride reacts with atmospheric moisture to produce unstable Si-OH bonds. Such moisture-exposed polymers exhibit poor stability during subsequent storage and melt spinning (a procedure employed in producing ceramic fibers from the polymer). The increased oxygen content adversely affects the elastic modulus of the ceramic fiber. The presence of ammonium chloride solid produces flaws in the ceramic fiber which can adversely affect the tensile strength of the fiber.
The patent literature discloses the preparation of amine and ammonia derivatives of methylpolysilanes (MPS) with somewhat reduced chloride content. Baney, et al., U.S. Pat. No. 4,314,956 discloses the synthesis of amine derivatives of methylpolysilanes via the aminolysis of the corresponding chlorine substituted methylpolysilanes. The methylpolysilanes are low molecular weight polymers having continuous silicon atoms along the backbone of the polymer. Chlorine substituted methylpolysilane polymers contain CH.sub.3 Si.tbd. units and (CH.sub.3).sub.2 Si.dbd. units wherein the valence sites which are not filled by bonds to other silicon atoms are satisfied by bonds to chlorine. Baney, et al. teaches a process for reacting the chlorine substituted methylpolysilane polymer with an aminolysis reagent of the formula NHR.sub.2 wherein R is hydrogen, an alkyl group, or phenyl. The Baney, et al. process is described as effecting the substitution of --NR.sub.2 for at least a portion of the chlorine atoms in the methylpolysilane polymer.
The methylpolydisilylazane (MPDZ) polymer of this invention has two silicon atoms alternating with a nitrogen atom along the backbone of the polymer chain. Methylpolydisilylazane polymers typically contain 3 to 5% by weight of chlorine substituents but also may be crosslinked or branched by additional nitrogen atoms bonded to silicon atoms along the backbone chain. Ammonia derivatives of methylpolysilanes prepared by the process described in Baney, et al. are pyrophoric while the ammonia derivatives of methylpolydisilylazanes of this invention are not pyrophoric.